Imperfect Images
No telescope can form a perfect image. Even if a reflecting telescope could have a perfect mirror, or a refracting telescope could have a perfect lens, the effects of aperture diffraction are unavoidable. In reality, perfect mirrors and perfect lenses do not exist, so image aberrations in addition to aperture diffraction must be taken into account. Image aberrations can be broken down into two main classes, monochromatic, and polychromatic. In 1857, Philipp Ludwig von Seidel (1821–1896) decomposed the first order monochromatic aberrations into five constituent aberrations. They are now commonly referred to as the five Seidel Aberrations.
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Famous quotes containing the words imperfect and/or images:
“I do not wish to see John ever again,—I mean him who is dead,—but that other, whom only he would have wished to see, or to be, of whom he was the imperfect representative. For we are not what we are, nor do we treat or esteem each other for such, but for what we are capable of being.”
—Henry David Thoreau (1817–1862)
“How clean the sun when seen in its idea,
Washed in the remotest cleanliness of a heaven
That has expelled us and our images . . .
The death of one god is the death of all.
Let purple Phoebus lie in umber harvest,
Let Phoebus slumber and die in autumn umber....”
—Wallace Stevens (1879–1955)